Key mechanism of metal transfer and characteristic of cavity evolution during SAW using in-situ X-ray imaging method

Abstract

The metal distribution and transfer during submerged arc welding (SAW) were investigated using in situ X-ray high-speed imaging method. The flux-wall droplet transfer mode was observed for the first time in SAW using a 1.6 mm diameter 308 L wire and the repelled droplet transfer mode and short circuit droplet transfer mode are also confirmed as the three fundamental modes. As the unique forces in the SAW, the supporting force and viscous resistance by the flux wall to the droplet affect the droplet geometry feature and transfer mode. These two forces are determined by the geometrical morphology of the cavity. As the welding speed increases from 1.5 mm/s to 4 mm/s, the proportion of short circuit transfer mode decreased from 70.69% to 3.64% while the repelled droplet transfer mode increased from 3.45% to 96.36% due to the reduction of cavity volume. The proportion of flux-wall transfer mode initially increased and then decreased. It reached the highest as the vertical cavity formed at the welding speed of 2 mm/s. Once the welding speed exceeds 4 mm/s, the flux-cored droplet transfer mode disappeared. The proportion of the other two tends to be stable because of an almost unchanged cavity volume.